Wafer de-chucking

ABSTRACT

A carrier head ( 100 ) for a CMP tool, wherein the membrane ( 108 ) defining a chamber with a contact surface ( 102 ) of the carrier head ( 100 ) has a number of integral tubes ( 110 ) termining in openings coupled directly to the substrate ( 106 ), in addition to a main fluid flow passage ( 104 ) coupled to the chamber defined by the membrane ( 108 ). In use, during loading and polishing, a vacuum is applied to the main fluid flow passage ( 104 ) and the tubes ( 110 ) to hold the substrate ( 106 ) in flat engagement with the membrane ( 108 ) and contact surface ( 102 ). In order to unload the substrate ( 106 ), fluid pressure is applied to the substrate ( 106 ) via the tubes ( 110 ), whilst maintaining the application of the vacuum via the main fluid flow passage ( 104 ) so as to minimise bending and breakage of the substrate ( 106 ).

This invention relates generally to to a carrier head and, more particularly, to a carrier head and membrane for chemical mechanical polishing apparatus.

Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited and etched, the outer or uppermost surface of the substrate, i.e. the exposed surface of the substrate, becomes increasingly nonplanar. This nonplanar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This method of planarization typically requires that the substrate be mounted on a carrier or polishing head. During polishing, the carrier head brings the exposed surface of the substrate into contact with a rotating polishing pad and provides a controllable load on the substrate to push it against the polishing pad. A typical carrier head includes a flexible membrane with an inner surface that encloses a chamber and an outer surface that provides a substrate mounting surface. By controlling the pressure in the chamber, the load applied to the substrate can be varied.

Referring to FIG. 1 a of the drawings, a typical CMP apparatus comprises one or more carrier heads 10 having a flexible membrane 12 sealed around an inner surface of the carrier head 10, so as to define a chamber. A gas or fluid inlet/outlet 14 is defined in the carrier head 10 which is in fluid communication with the membrane 12. A pressure control assembly (not shown) is provided for drawing air from the chamber defined by the membrane 12 or blowing air into the chamber.

In use, a substrate 16 is loaded into the carrier head 10 by bringing it into contact with the membrane 12, and then a vacuum is created via the outlet 14 to hold the membrane 12 and the substrate 16 flat against the inner surface of the carrier head. During actual polishing, the vacuum is maintained and the carrier head 10 lowers the substrate 16 into contact with a polishing pad 18, and a slurry acts as the media for chemical mechanical polishing of the substrate (or wafer) 16. Thus the carrier head 10 loads and holds the substrate 16 against the polishing pad 18. It will be appreciated by a person skilled in the art that FIG. 1 a is a schematic diagram for illustrative purposes and that the polishing pad 18 usually has a larger diameter than the head 10. During polishing, the pad 18 is also in contact with the head via a peripheral retaining ring which keeps the wafer from slipping away during polishing. In addition, during polishing, wafer is pressed against the pad by applying pressure to the membrane through the inlet 14.

Referring to FIG. 1 b of the drawings, during unloading (or de-chucking) of a wafer 16 from the carrier head 10 of a CMP tool, air is blown, via the inlet 14, into the chamber defined by the membrane 12 so as to inflate it. In theory, this process is intended to cause the wafer 16 to become dislodged from the membrane 12. However, in practice, depending on the adhesion between the wafer 16 and the membrane 12, the wafer may bend and there is an increased risk that it may break. This risk is especially aapparent if there are scratches on the wafer 16.

US Patent Application Publication no. 2003 236056 A1 describes an arrangement whereby lateral sprays are used to assist wafer unloading by spraying fluid or gas between the wafer and the membrane. In addition, there are lateral pins or blades (inserted between the wafer and the membrane) that further assist by pulling the wafer down. The disadvantage is that sprays may cause the wafer to be blown in an undesired lateral direction if they are not well balanced on all sides, and blades have an inherent risk of breaking the wafer if the wafer sticks to the membrane.

It is therefore preferred to provide a carrier head and membrane arrangement in general and for a CMP tool in particular, whereby efficient unloading of a wafer from the carrier head is achieved with reduced risk of breakage relative to prior art arrangements.

In accordance with the present invention, there is provided a carrier head for a chemical mechanical polishing apparatus, the carrier head comprising a contact surface on which is provided a membrane for receiving a substrate to be polished, said membrane forming a chamber with said contact surface, the carrier head further comprising a main fluid flow passage coupled at one end to said chamber and at an opposite end to means for creating a vacuum between said membrane and said contact surface, said membrane comprising at least one opening from which extends a respective fluid flow channel for selectively applying a vacuum or fluid pressure directly to said substrate, when in use.

In a preferred embodiment, the respective fluid flow channel that extends from the at least one opening in said membrane comprises an integral tube. In a preferred embodiment, the carrier head comprises a respective guide passage for receiving the or each fluid flow channel. Beneficially the or each fluid flow channel is received within a respective guide passage in slidable engagement, such that movement of the membrane is not restricted during polishing. In a preferred embodiment, the carrier head comprises a plurality of concentric guide passages for receiving a plurality of respective fluid flow channels extending from respective openings in said membrane. Said main fluid flow passage is preferably generally central relative to said contact surface and substrate and said one or more membrane openings and respective fluid flow channels are preferably off-centre relative to said contact surface and substrate.

The present invention extends to a flexible membrane for use with a carrier head as defined above for forming a chamber with said contact surface, the membrane comprising one or more openings from the or each of which extends a respective fluid flow channel.

Also in accordance with the present invention there is provided a method of performing chemical mechanical polishing in respect of a substrate, comprising the steps of providing a carrier head as defined above, loading a substrate onto the contact surface said carrier head, against said membraine via main fluid flow passage, performing chemical mechanical polishing in respect of said substrate, and unloading said substrate by applying fluid pressure thereto via said at least one opening and respective fluid flow channel whilst maintaining the application of a vacuum to said membrane via said main fluid flow passage.

Preferably, during loading of said substrate, a vacuum is additionally applied to said substrate via said at least one opening and respective fluid flow channel.

The present invention extends to a fluid pressure control system for performing the method defined above in a carrier head as defined above, the fluid pressure control system comprising an outlet coupled to said main fluid flow passage and said one or more fluid flow channels, and being configured to operate in a first loading mode, wherein a vacuum is applied to said main fluid flow passage and said one or more fluid flow channels for loading said substrate onto said carrier head and performing chemical mechanical polishing in respect thereof, and a second, unloading mode, wherein a vacuum is applied to said main fluid flow passage and fluid pressure is applied to said one or more fluid flow channels for unloading said substrate from said carrier head.

These and other aspects of the present invention will be apparent from, and elucidated with reference to the embodiments described herein.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

FIG. 1 a is a schematic cross-sectional side view illustrating the principal components of a carrier head of a CMP tool according to the prior art, when a wafer has been loaded;

FIG. 1 b is a schematic cross-sectional side view of the carrier head of FIG. 1 a during unloading of the wafer;

FIG. 2 is a schematic side view illustrating the principal components of a carrier head according to an exemplary embodiment of the present invention; and

FIG. 3 is a schematic view of a membrane for use with the carrier head of FIG. 2;

Referring to FIGS. 2 and 3 of the drawings, a carrier head 100 according to an exemplary embodiment of the present invention comprises an inner contact head 102 having a generally central main inlet/outlet 104 for generating the vacuum required to hold the wafer 106 flat against the membrane 108 and the polishing pad (not shown) during polishing, as in the prior art arrangement described with reference to FIG. 1 of the drawings.

However, in this case, referring especially to FIG. 3 of the drawings, the membrane 108 is formed with a series of integral tubes 110, and the contact head 102 is provided with a corresponding series of slots or passages 112 for receiving the membrane tubes 110. The main inlet/outlet 104 and the membrane tubes 110 are connected to a fluid pressure control arrangement (not shown). Thus, in the assembled configuration illustrated schematically in FIG. 2 of the drawings, fluid flow through the main inlet/outlet 104 is coupled to the membrane 108, whereas fluid flow through the membrane tubes 110 is coupled directly to the wafer 106.

In use, as before, a substrate 106 is loaded into the carrier head 100 by bringing it into contact with the membrane 108, and then a vacuum is created via the outlet 104 and the membrane tubes 110 to hold the membrane 108 and the substrate 106 flat against the inner surface of the contact head 102. During actual polishing, the vacuum is maintained and the carrier head 100 lowers the substrate 106 into contact with a polishing pad (not shown). Subsequently, gas or fluid pressure is applied through inlet/outlet 104, which applies a pressure between the wafer 106 and the polishing pad, and a slurry acts as the media for chemical mechanical polishing of the substrate (or wafer) 106. Thus the carrier head 100 loads and holds the substrate 106 against the polishing pad. When the polishing process has been completed, the vacuum is re-applied through the inlet/outlet 104 so as to enable the carrier head 100 to lift the substrate 106 away from the polishing head.

In this case, however, when it is required to unload (or de-chuck) the substrate 106 from the carrier head 100, fluid (e.g. air) pressure is applied by the fluid pressure control arrangement directly to the substrate surface, via the membrane tubes 110, whilst the vacuum continues to be maintained via the main inlet/outlet 104 on the membrane 108. In this manner, the air pressure, applied directly to the wafer 106 overcomes the adhesive forces between the wafer 106 and the membrane 108 and causes the wafer 106 to be released, while the continued vacuum provided via the main inlet/outlet 104 prevents signfiicant inflation of the membrane 108, and therefore prevents signficant bending of the wafer 106.

The membrane tubes 110 are not affixed to the corresponding guide passages 112 in the contact head 102. As such, the membrane tubes 110 are mounted for slidable movement within the guide passages 112 and membrane movement is thus substantially unrestricted during polishing.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word “comprising” and “comprises”, and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein one component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in FIG. 3, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

A person skilled in the art will readily appreciate that various parameters disclosed in the description may be modified and that various embodiments disclosed and/or claimed may be combined without departing from the scope of the invention.

It is stipulated that the reference signs in the claims do not limit the scope of the claims, but are merely inserted to enhance the legibility of the claims. 

1. A carrier head for a chemical mechanical polishing apparatus, the carrier head comprising a contact surface on which is provided a membrane for receiving a substrate to be polished, said membrane forming a chamber with said contact surface, the carrier head further comprising a main fluid flow passage coupled at one end to said chamber and at an opposite end to means for creating a vacuum or applying fluid pressure between said membrane and said contact surface, said membrane comprising at least one opening from which extends a respective fluid flow channel for selectively applying a vacuum or fluid pressure directly to said substrate, when in use.
 2. A carrier head according to claim 1, wherein the respective fluid flow channel that extends from the at least one opening in said membrane comprises an integral tube.
 3. A carrier head according to claim 1, comprising a respective guide passage for receiving the or each fluid flow channel.
 4. A carrier head according to claim 3, wherein the or each fluid flow channel is received within a respective guide passage in slidable engagement.
 5. A carrier head according to claim 3, comprising a plurality of concentric guide passages for receiving a plurality of respective fluid flow channels extending from respective openings in said membrane.
 6. A carrier head according to claim 1, wherein said main fluid flow passage is generally central relative to said contact surface and substrate and said one or more membrane openings and respective fluid flow channels are off-centre relative to said contact surface and substrate.
 7. A flexible membrane for use with a carrier head according to claim 1, for forming a chamber with said contact surface, the membrane comprising one or more openings from the or each of which extends a respective fluid flow channel.
 8. A method of performing chemical mechanical polishing in respect of a substrate comprising the steps of providing a carrier head according to claim 1, loading a substrate onto the contact surface said carrier head against said membrane, and applying a vacuum to said membrane via main fluid flow passage performing chemical mechanical polishing in respect of said substrate, and unloading said substrate by applying fluid pressure thereto via said at least one opening and respective fluid flow channel whilst maintaining the application of a vacuum to said membrane via said main fluid flow passage.
 9. A method according to claim 8, wherein during loading of said substrate, vacuum is additionally applied to said substrate via said at least one opening and respective fluid flow channel.
 10. A fluid pressure control system for performing the method of claim 8, in a carrier head according to claim 1, the fluid pressure control system comprising an outlet coupled to said main fluid flow passage and said one or more fluid flow channels and being configured to operate in a first, loading mode, wherein a vacuum is applied to said main fluid flow passage and said one or more fluid flow channels for loading said substrate onto said carrier head and performing chemical mechanical polishing in respect thereof, and a second, unloading mode, wherein a vacuum is applied to said main fluid flow passage and fluid pressure is applied to said one or more fluid flow channels for unloading said substrate from said carrier head. 